I replaced the coil today. No change. Never seemed any different or moisture dependent. That being said, it is always 100% humidity here.

I also took the the EGR valve off and vacuum tested it and the like. I put it back on and removed the exhaust line that went to it. It didn't have any noticeable pressure. Revving up made no difference in park. In drive with the brakes on and my wife in the car giving it a little gas it opened up as expected. I don't really think the EGR valve is the problem since what I did to troubleshoot it would have fixed it if that was the issue.

Given that since the problem began I have changed the spark plugs, coil, wires, fuel filter, checked for vacuum leaks using propane - no apparent leak. It seems the EGR is working correctly, so I think the torque program has incorrect parameters. It gives it a pass and a fault for the same reading in two different options. The EGR appears to work correctly and there is certainly plenty of air moving through it, the manifold, and through the EGR when it operates. Vacuum is good. Id be lying if I said I understood exactly how the DPFE would impact the idle if it were bad. Would it?

I guess my next option is to hook up my intake cleaner to it and give it a try on the off chance that cleaning the intake/injectors will make a difference. I'm going to pull the plugs first and see how they look. I'll probably go ahead and swap out the air filter too. It is about due.

I could see a rough perceived idle being caused by the motor mounts... is there anyone with a 4.2 that could check and see what RPM range their idle at with ac on and off? Maybe I am just feeling a shake because the motor mounts need replaced...?

 

The 4.2 shouldn't shake because it's an even firing engine and has a balance shaft.

 

I'll check shortly and use my scan gauge to get the exact rpms.

 

Here you go. Trucks not fully warmed up, it's at about 130° with 180° - 192° being the normal operating temp.

 

Thanks 2008. Mine will idle good for 5 seconds and then stumble, recover, run rough off and on for a few seconds and then run ok again. It drives fine still. I am assuming it happened slowly because it didn't just happen one day or anything. I only noticed because someone pointed out that it idled rough. I never noticed to be honest - but I did notice that it would vibrate going uphill in high gear when I just gave it a little more gas.

I'm running out of things to check and do. Tomorrow is my first day off in a while and I'm going to be messing with it for at least a couple hours.

 

Not a problem. How far do the rpms drop when it stumbles?

 

It has about a 175 RPM swing. It drops down to 650 and then catches up and moves back to 750ish. Sometimes it goes to 825. I think I can make a chart with torque to map the actual rpm. I'll do that today.

 

I drove about 50 miles with a few cans of Berrymans B12 in 1/4 tank of gas. Definite improvement in how it drives. It could just be the boost in octane with what was left when I filled it up. It does idle better with the AC on now though.

I couldn't get torque to send the chart. I am idling around the same as you though. The issue is that every 5-10 seconds it will drop down to about 600 and then go back up to 850 and then bounce back and force between 750-800 before leveling out and running correctly for another 5-10 seconds.

After running the Berryman's through it, it it doesn't jump back and force as much with the AC on, it just has a rough idle. It is driving fine. I haven't had a chance to pull the plugs back out and check them yet.

I'm really starting to believe this might be a problem with one of the little sensors getting to be lame but not completely dead yet.

 

2008XL, can you look at your test results and see what you get for these tests?


MID:$32 TID:$82
- EGR Monitor Bank 2
Max: -32.659kPa Min: -32.768kPa
Test result value: 0.646kPa
FAIL
----
MID:$32 TID:$83
- EGR Monitor Bank 2
Max: 32.767kPa Min: -3.561kPa
Test result value: 0.646kPa
PASS
----
MID:$32 TID:$84
- EGR Monitor Bank 2
Max: 5.001kPa Min: -32.768kPa
Test result value: 0.767kPa
PASS
----
MID:$32 TID:$85
- EGR Monitor Bank 2
Max: 32.767kPa Min: 1.494kPa
Test result value: 5.949kPa
PASS

 

Well, I figured I will go ahead and give the spark plugs a change. They are about $5 a piece shipped on ebay for motorcraft. I looked it up on advanced and autozone and they were about the same. Then I found a coupon for $20 off $50 purchase at advanced auto. For $33 I got the 6 spark plugs and a air filter. I figure that is a win since I needed to change the air filter anywho.

 

Hey, sorry, I was on vacation in Florida and didn't even see this! What did you use to test your results?

 

Dur, I forgot everyone doesn't have the Torque app. lol. I just went into the code reader and looked through the reported information.


Where did you go in Florida?

 

I only have a scanguage II and I don't believe it can do any of that, unfortunately.

I was in Homosassa, Ft. Myers, Delray Beach and Orlando.

 

I can confirm that 2008 XL's readings are absolutely correct. My RPM swing is the exact same according to my SGII.

 

I changed the air filter and spark plugs today. I got motorcraft(they were gapped in the box at 44, so I regapped them. I thought they were supposed to be pregapped?) and put the old wires back on. Nothing is different. The sparkplugs I took out looked fine.

I did notice that If I rev it quickly and let off it will make a tiny backfire type noise out the exhaust.